Schizophrenia is a common, devastating neuropsychiatric disorder whose etiology is largely unknown. Multiple studies in humans and in mouse and fly models suggest a role for proline and PRODH, the gene encoding the first enzyme in the pathway of proline catabolism, in contributing risk for schizophrenia. Other studies, however, reach contradictory conclusions. Here, we provide a critical review of the data in the context of what is known about proline metabolism and suggest studies for the future. Overall, there is considerable evidence supporting a role for certain loss of function PRODH variants conferring risk for schizophrenia in some individuals.